In the art of hydrocyclones, commonly referred to as cyclones, a free vortex principle is used for separating and classifying suspended solids, for example, to separate solids from water so that the water may be reused or for separating mud and slime from pulverized coal or for classifying oil drilling muds. Cyclones are also commonly used to separate sand, grit, bark particles and shives from cellulose fibers in the production of a paper making slurry.
In an effort to utilize more of the cellulose in trees, there is a trend in the paper making industry to chip whole trees including the trunks, branches and twigs. Since it is not practical to debark the branches and twigs, the bark is cooked with the chips and must be removed after cooking, even for grades of paper not generally requiring such cleaning. Since a cyclone becomes more efficient with respect to the removal of fine particles as the major diameter of the cyclone decreases, it has become desirable to employ a larger number of smaller cyclones such as cyclones having an inner diameter of six inches or less. The improved efficiency of the smaller cyclones may be partially sacrificed to permit a much lower pressure drop across the cyclones, and the lower pressure drop provides for a significant decrease in the energy required for operating the cyclones so that there is a significant savings in the cost of operating the cyclones, especially when millions of gallons of liquid or fluid are treated per day.
There have been a number of methods either used or proposed for assembling a group of relatively small cyclones into a cluster so as to minimize the space required by the assembly and to provide for a more compact and economic construction. For example, U.S. Pat. No. 3,335,860 disclose a cluster arrangement of cyclones which are arranged in a spoke type manner within a circular cast metal housing. Preferably, the cyclones disclosed in this patent are each formed of a ceramic material for obtaining a maximum service life. U.S. Pat. No. 3,415,374 discloses other cluster arrangements of hydrocyclones which are arranged either radially within an annular pattern or in a rectangular pattern with the axes of the cyclones in parallel relation. U.S. Pat. No. 3,543,931, which issued to the applicant of the present invention, shows another form of arranging cyclones in parallel spaced relation. In addition, a cluster arrangement of hydrocyclones is manufactured by A. B. Fractionator of Stockholm, Sweden and marketed under the trademark "Albia 100". This cleaning device incorporates a cluster arrangement of tubular cyclones arranged in parallel relation. Each cyclone extends through a set of resilient ring seals mounted within aligned holes formed in parallel spaced plates or walls which define chambers therebetween in a manner similar to that shown in above U.S. Pat. No. 3,415,374.